The use of fertilizers to enhance plant and crop production and overcome poor soil quality is widespread. Most commonly employed commercially available nitrogen containing fertilizers are inorganic chemical fertilizers such as urea. The extended use of urea is often associated with negative environmental consequences, such as nitrate contamination in run off and ground water, and emission of ammonia and nitrous oxide to the atmosphere. Attention to nitrogen fertilizer application has shifted from the role of promoting crop production to alleviating environmental pollution. There are a variety of new management practices and technologies that can promote nitrogen use efficiency and alleviate environmental pollution.
One of the widely used technologies is the application of a urease inhibitor in combination with the urea treatment. The urea component of fertilizer applied to the soil becomes a source of ammonia as a result of urease catalyzed hydrolysis of urea, an enzyme produced by numerous fungi and bacteria that is well known to skilled artisans. Urease inhibitors can slow down the conversion rate of urea to ammonia, thereby significantly reducing the quantity of urea that otherwise has to be applied on the soil by reducing the amount of ammonia volatilization. One of the most common urease inhibitors is N-(n-butyl) thiophosphoric triamide (NBPT) (See e.g. U.S. Pat. No. 5,698,003).
Another widely used technology is the application of nitrification inhibitors to significantly reduce nitrate leaching and gaseous nitrogen emissions. Most nitrogen supplied as a commercial fertilizer is ultimately transformed to a nitrate form of nitrogen. In the presence of adequate oxygen, warm temperatures, and some moisture, ammonium-N is converted to nitrate-N through a biochemical process known as nitrification that requires two forms of soil bacteria. The first bacterium Nitrosomonas converts ammonium-N to nitrite-N. The second bacterium Nitrobacter converts nitrite-N to nitrate-N. Nitrification inhibitors have one primary way of delaying the nitrification process by inhibiting the bacteria Nitrosomonas in the area where ammonium is to be present. Some widely used nitrification inhibitors that are commercially available include 2-chloro-6-(trichloromethyl)-pyridine (Nitrapyrin) and dicyandiamide (DCD).
In addition to the application of chemical enzyme inhibitors such as urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) and nitrification inhibitors such as dicyandiamide (DCD), fertilizer compositions comprising microorganisms (so-called “bio-fertilizers” or “bio-stimulants”) are increasingly considered as alternatives to conventional chemical fertilizers. The ability of specific bacterial species to promote plant growth has long been recognized. For example, nitrogen-fixing bacteria such as Rhizobium species provide plants with essential nitrogenous compounds. Species of Azotobacter and Azospirillum have also been shown to promote plant growth and increase crop yield, promoting the accumulation of nutrients in plants. However bacteria of these genera are often unable to compete effectively with native soil and plant flora, thereby requiring the application of impractically large volumes of inocula.